Endpoint Detection Method Research Articles

Cu(In,Ga)Se<sub>2</sub> Prepared by a 2 and 3-Stage Hybrid RF-Magnetron Sputtering and Se Evaporation Method: Properties and Solar Cell Performance

The potential of RF-magnetron sputtering to achieve high quality Cu(In,Ga)Se2 (CIGS) thin films and efficient solar cells with the goal of using a single technique for all solar cell processing steps is explored. The end point detection method was adapted to RF-magnetron deposition of CIGS in two- or three stages sputtering process. It allows the control of the final composition of the deposited layers in a reproducible way. The influence of substrate temperature and Ar pressure during the deposition on the surface and crossectional morphology of CIGS films was studied for two and three-stage sputtering process sequence. The solar cells prepared with films deposited by two-stage sputtering nave showed a better performance with maximum efficiency above 8 %.

Cytotoxic and antimitotic effects of N‐containing Monascus metabolites studied using immortalized human kidney epithelial cells

Recently the first Monascus metabolites with a pyridine ring were detected, the monascopyridines A and B. They are formally dehydrogenated derivatives of the red rice pigments rubropunctamine and monascorubramine. Because of their structural similarity, the toxicological effects of these secondary metabolites were studied using immortalized human kidney epithelial cells. The cytotoxicity was determined with the following different endpoint detection methods: metabolic activity, trypan blue exclusion, and electronic cell counting. The compounds led to EC(50) values between 11 and 31 micromol/L but the pigments caused a stronger reduction of the cell viability. Also, the apoptotic potential was examined by measuring caspase 3 activity and detecting apoptotic bodies, but none of the tested compounds induced apoptosis. All four substances caused a rise of the mitotic index to about 9% (100 micromol/L monascopyridine A and B) and 20% (25 micromol/L rubropunctamine and monascorubramine). The significant decrease of the ratio of cells in the ana- and telophase to cells in the prometa- and metaphase proved a stop of the mitosis at the meta- to anaphase control point. The compounds caused mitotic arrest and the formation of structural damages like c-mitosis through interaction with the mitotic spindle. These effects point to an aneuploidy inducing potential, which is linked to cancer formation.

Direct Focused Ion Beam Drilling of Nanopores

AbstractFocused 30keV gallium ion beam, single-pixel drilling combined with backside particle detection is used to fabricate pores having exit diameters as small as ~11 nm in 200 nm-thick silicon nitride membranes. The backside channelplate detector response obtained about the onset of breakthrough is interpreted by plan-view transmission electron microscopy investigations of hole morphology. Immediately prior to breakthrough, there is a rise in detector signal as the local membrane thickness is reduced. This likely occurs as a result of ion transmission and, possibly, forward sputtering. At the dose required for breakthrough a maximum detector signal is obtained thus providing a potential method for end point detection. The focused ion drilling technique avoids broad area beam exposure methods that are often used to reduce hole diameter to nanometer dimension. In addition, the current approach overcomes difficulties in determining a required dose for breakthrough such as those that arise from an inhomogeneous membrane thickness, redeposition, or ion channeling.

An intra-operative vibrational method for hip stem insertion endpoint detection and stability assessment—a pilot study

An intra-operative vibrational method for hip stem insertion endpoint detection and stability assessment—a pilot study

Superconducting quantum interference phenomenon inBi2Sr2CaCu2O8+δsingle crystals

The operational direct-current superconducting quantum interference device (dc-SQUID) based on intrinsic Josephson junctions in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ high-${T}_{c}$ superconductor is fabricated and studied. The in-plane loop layout and the developed in situ end-point detection method allowed an accurate control of the number of junctions in the SQUID. A clear periodic modulation of the superconducting current as a function of magnetic flux through the SQUID loop is observed. This is an unambiguous evidence for the quantum interference phenomenon in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals.

Automated methods for multiplexed pathogen detection

Detection of pathogenic microorganisms in environmental samples is a difficult process. Concentration of the organisms of interest also co-concentrates inhibitors of many end-point detection methods, notably, nucleic acid methods. In addition, sensitive, highly multiplexed pathogen detection continues to be problematic. The primary function of the BEADS (Biodetection Enabling Analyte Delivery System) platform is the automated concentration and purification of target analytes from interfering substances, often present in these samples, via a renewable surface column. In one version of BEADS, automated immunomagnetic separation (IMS) is used to separate cells from their samples. Captured cells are transferred to a flow-through thermal cycler where PCR, using labeled primers, is performed. PCR products are then detected by hybridization to a DNA suspension array. In another version of BEADS, cell lysis is performed, and community RNA is purified and directly labeled. Multiplexed detection is accomplished by direct hybridization of the RNA to a planar microarray. The integrated IMS/PCR version of BEADS can successfully purify and amplify 10 E. coli O157:H7 cells from river water samples. Multiplexed PCR assays for the simultaneous detection of E. coli O157:H7, Salmonella, and Shigella on bead suspension arrays was demonstrated for the detection of as few as 100 cells for each organism. Results for the RNA version of BEADS are also showing promising results. Automation yields highly purified RNA, suitable for multiplexed detection on microarrays, with microarray detection specificity equivalent to PCR. Both versions of the BEADS platform show great promise for automated pathogen detection from environmental samples. Highly multiplexed pathogen detection using PCR continues to be problematic, but may be required for trace detection in large volume samples. The RNA approach solves the issues of highly multiplexed PCR and provides “live vs. dead” capabilities. However, sensitivity of the method will need to be improved for RNA analysis to replace PCR.

지시약 적정법 및 분광광도법에 의한 양이온 고분자 전해질의 전해밀도 정량

Polyelectrolyte titration, which was called colloid titration is based on the stoichiometric reaction between oppositely charged polyelectrolytes, This can be used, for instance, to determine the charge density of a cationic polyelectrolyte, using an anionic polyelectrolyte of known charge density, such as potassium polyvinyl sulfate (PPVS). The technique requires a suitable method of end-point detection and there are several possibilities. In this work, two methods have been investigated: visual titrimetry based on the color change of a cationic dye (o-toluidine blue, o-Tb) and spectrophotometry based on the absorbance change corresponding to the color change of the same dye. These have been applied to several cationic polyelectrolytes with different charge density and molecular weight. In all cases, the cationic charge was due to quaternary nitrogen groups. In the case of cationic dye, it was shown that the sharpness depends on the charge density of cationic polyelectrolyte. With the polyelectrolytes of lower charge density, the binding to PPVS is weaker and binding of the dye to PPVS can occur before all of the polyelectrolyte charge has been neutralized. However, by carrying out titrations at several polyelectrolyte concentrations, good linear relationships were found, from which reliable charge density values could be derived. Effects of pH and ionic strength were also briefly investigated. For cationic polyelectrolytes (copolymers of acrylamide and dimethylaminoethy] acrylate), there was some loss of charge at higher pH values, probably as a result of hydrolysis. Increasing ionic strength causes a less distinct color change of o-Tb, as a result of weaker electrostatic interactions.

Broadband optical end-point detection for linear chemical–mechanical planarization (CMP) processes using an image matching technique

In this paper we discuss an end-point detection (EPD) method for the dielectric linear chemical–mechanical planarization (CMP) processes. The proposed EPD algorithms utilize the interferometry optical signals to determine the post-CMP film thickness. A set of collected broadband spectral signals are formed as a spectral image. An image-matching technique is then used to match the processed signal image to the reference image template obtained at the target film thickness. Several matching criteria are discussed and compared. We find that the image correlation coefficient is a good indicator to determine the process end-point. We also consider the impact of the material removal rate variations on the interferometry spectral signals. An analytical calculation is carried out to find an extraction and compression searching range of the spectral image to compensate for the removal rate uncertainties. The correctness and effectiveness of the proposed algorithms have been demonstrated through applications to an inter-metal dielectric (IMD) device CMP process. Compared with other optical EPD methods, the proposed image-matching method is robust to the CMP process variations.

In Situ Endpoint Detection by Pad Temperature in Chemical–Mechanical Polishing of Copper Overlay

As the number of metal levels and the wafer size increase, the global planarity and effective removal of metal overlay across the wafer becomes more crucial. Chemical-mechanical polishing (CMP) has been recognized essential to achieve this goal. Accurate in situ endpoint detection and monitoring method significantly improves the yield and throughput. Previous methods have been proposed, which either require the rearrangement of the machine set-up, or can only be implanted on certain types of machines. In this study, a model for pad temperature capable of predicting the endpoint of CMP in situ is established based on the total consumed kinematic energy between wafer and pad. Limited assumptions of thermal and kinematic conditions are made. The model of temperature rise uses the integral of the relative polishing speed and is verified by on-line measurement. Since the coefficient of friction between the pad and dielectric layer is distinguishably lower than that between the pad and the metal layer, the pad temperature increases milder than polishing the metal layer. In use of the proposed regression method applied to the measured temperature rise, the endpoint of the process can be detected.

Low-temperature deposition of Cu(InGa)Se2 solar cells on various substrates

Abstract Thin films of Cu(In,Ga)Se2 were deposited at substrate temperatures (Tss) of 550°C and 350°C on soda-lime glass/Mo and titanium foil/Mo. The effects of these parameters on the physico-chemical, optical and electrical properties of the films were studied as well as the influence of an alkaline source in the films. The control of the composition of the films using the end point detection method was also studied. Solar cells were then fabricated and the influences of the same parameters were analyzed. Efficiencies ranged from above 12% on both substrates at 550°C in the presence of Na to 10% on Ti without Na. Lower efficiencies were obtained at 350°C due in part to difficulty with the end point detection technique and in part to smaller grain sizes.

Continuous Speech Recognition without End-point Detection

A new continuous speech recognition method that does not need the explicit speech end-point detection is proposed. A one-pass decoding algorithm is modified to decode the input speech of infinite length so that, with appropriate non-speech models for silence and ambient noises, continuous speech recognition can be executed without the explicit end-point detection. The basic algorithm 1) decodes a processing block of the predetermined length, 2) tracebacks and finds the boundaries of the processing blocks where the word history in the preceding processing block is merged into one, and 3) restarts decoding from the boundary frame with the merged word history. The effectiveness of the method is verified by the spoken dialogue transcription experiments. With a 5-minute dialogue in a moving car, the proposed method gives better results in word accuracy than the results using the explicit end-point detection method and the conventional one-pass decoder.

Motor-Current-Based Real-Time End Point Detection of Shallow-Trench-Isolation Chemical Mechanical Polishing Process Using High-Selectivity Slurry

We have studied the chemical mechanical polishing (CMP) of a shallow-trench-isolation (STI) structure in 0.18 µm semiconductor device fabrication. CMP is applied for the STI structure with and without a reverse moat pattern. The real-time end point detection (EPD) method based on the motor current (MC) signal is tested, and the factors affecting the conventional motor current detection method are investigated. The results showed that the EPD method could not be applied to STI-CMP with a reverse moat etch process due mainly to the pad conditioning effect and the characteristics of an open nitride structure. In the case of direct STI-CMP without a reverse moat etch process, global planarization with low defect levels can be achieved using a high-selectivity slurry (HSS) with a high selectivity for SiO2 and Si3N4, and the EPD method shows acceptable and reproducible results.

Molecular beacons as diagnostic tools: technology and applications.

Molecular beacons are single-stranded, fluorophore-labeled nucleic acid probes that are capable of generating a fluorescent signal in the presence of target, but are dark in the absence of target. Molecular beacons allow multiplex detection of PCR products in real time in a homogeneous assay format. Real time detection is inherently quantitative and affords a greater dynamic range than end-point detection methods. Reactions in a homogeneous assay format are sealed before amplification takes place, providing improved contamination control. A single cycler/reader instrument, coupled with automated sample preparation, results in higher throughput and greater ease of use. A multiplex qualitative assay that detects Chlamydia trachomatis and Neisseria gonorrhoeae, along with an internal control, has been developed. High specificity is achieved through careful selection of primers, probes and assay conditions. Quantitative HIV, HCV, and HBV viral load assays, with sensitivities of 50 copies/ml, 20 IU/ml, and 50 copies/ml, respectively, are achievable. The viral load assays are designed to quantitate all subtype and genotype specimens equivalently. A molecular beacon assay has been designed to detect a single nucleotide polymorphism in the beta2 adrenergic receptor gene.

A comprehensive review of endpoint detection in chemical mechanical planarisation for deep-submicron integrated circuits manufacturing

As the number of metal levels and the wafer size increase, the need for global planarity across the wafer becomes more crucial. Chemical mechanical planarisation (CMP) is considered the key technique to achieve this goal. Accurate in situ end point detection and monitoring method can reduce the product variance, improve the yield and throughput. During CMP process, the wafer is brought downward against the polishing pad completely. The monitoring of the wafer polishing in such a configuration becomes a difficult task. Many methods have been proposed in the past years, including the optical, electrical, acoustical/vibrational, thermal, frictional, chemical/electrochemical methods and others, which are critically reviewed in this study. The mainstream of the industrial application and the future trend are investigated.

Signal analysis of the end point detection method based on motor current

We first studied the factors affecting the motor current (MC) signal. It was found to be strongly affected by systematic hardware noise depending on the polishing recipe, such as pad conditioning and arm oscillation. We then studied the end point detection (EPD) for the chemical mechanical polishing (CMP) process of the shallow trench isolation (STI) structure with a reverse moat pattern. The MC signal showed a high amplitude peak in the fore part caused by the reverse moat pattern. We also found that the end point (EP) could not be detected properly and reproducibly due to the pad conditioning effect, especially when a conventional low selectivity slurry was used. Even when there was no pad conditioning effect, the EPD method could not be applied, since the measured end point was always the same due to the characteristics of the open nitride structure.

Microscale Determination of Vitamin C by Weight Titrimetry

A laboratory experiment involving the quantitative microscale determination of ascorbic acid in pharmaceutical tablets of vitamin C by weight-titrimetry using (diacetoxyiodo)benzene as titrant and differential electrolytic potentiometry to locate the end-point is presented. The experiment affords an opportunity for students to explore nonconventional techniques such as the use of a novel organic oxidimetric titrant, titration in a semiaqueous medium, gravimetric titration, and an electrometric method of end-point detection using polarized electrodes. Synthesis, purification, and purity checking of the titrant may also be included in the project. Some advantages of the method are very low reagent consumption, low-cost equipment, improved sensitivity, and high precision and accuracy. Furthermore, the experiment will help the student to relate chemical analysis to everyday life.

Electrical impedance measurement as an endpoint detection method for routine coagulation tests

A whole-blood platelet aggregometer is adapted to measure electrical impedance changes in plasma during prothrombin time (PT) estimations. The impedance curve shows an acceleration phase, which is comparable to the absorbance curve acceleration phase associated with the onset of coagulation. The amplitude of the impedance change correlates with the fibrinogen concentration of the plasma. Statistical analysis of PT derived by absorbance and impedance changes shows a significant difference between the two methods but a good correlation. The method is reproducible but laborious and requires attention to technique. Further investigation of the method utilising a more sensitive instrument and redesigned electrodes is indicated. It may also be possible to modify reagent systems to optimise impedance changes.

End-point Detection of Reactive Ion Etching by Plasma Impedance Monitoring

For the practical application of end-point detection of etching using plasma-impedance monitoring, the factors determining the impedance were clarified using an electric circuit model of a reaction chamber. In the model, plasma is approximated by a conductor, and the floating capacitance and wafer of a powered electrode, as well as the powered-electrode sheath (the sheath formed between the plasma and powered electrode), are approximated by capacitors. Calculated values obtained using the model agree well with measured values obtained by an impedance monitor installed between the powered electrode and the matching network. Based on this result, it was inferred that the impedance depends on the powered-electrode sheath-voltage and electron density, as well as on the floating capacitance and area of the powered electrode, the dielectric constant and thickness of the wafer, and the electron temperature. Next, the end-point detection method of etching by impedance monitoring was applied to reactive ion etching of SiO2 films, and the following finding was confirmed: the change in the impedance significantly depends on the RF power and the exposed area ratio (the ratio of etched area to wafer area) on the wafer. In addition, the feasibility of detecting the point of change of the exposed area ratio on the wafer, where the area size varies during etching, by detecting microchanges in the impedance, was demonstrated. As a result, the possibility of highly accurate end-point detection of etching by impedance monitoring was confirmed.

Endpoint detection method for CMP of copper

A novel method to detect the endpoint during Cu-CMP has been developed. It is based on the determination of the Cu concentration within the slurry on the pad that has just polished the wafer. The measurement of the ion concentration is performed using a capillary and an ion-selective electrode. The endpoint of the CMP process is detected by the decrease of Cu ion concentration, which is displayed by an decreased potential at the electrode. An experimental set-up has been established which can be applied to a commercial polishing tool. The method has been tested under various process conditions. The new endpoint detection system revealed to work independently of the polishing tool and the wafer size.

Charge determination of synthetic cationic polyelectrolytes by colloid titration

The stoichiometric interaction between oppositely charged polyelectrolytes forms the basis of the technique of colloid titration. This can be used, for instance, to determine the charge density of a cationic polyelectrolyte, using an anionic polyelectrolyte of known charge density, such as potassium polyvinyl sulphate (PPVS). The technique requires a suitable method of end-point detection and there are several possibilities. In this work three methods have been investigated: visual observation of the colour change of a cationic dye ( o-toluidine blue), spectrophotometric determination of the colour change of the same dye, and electrokinetic detection of charge neutralisation, using a streaming current detector. These have been applied to a range of cationic polyelectrolytes, with different charge densities and molecular weights. In all cases, the cationic charge was due to quaternary nitrogen groups. In the case of the cationic dye, it was shown that the sharpness of the colour change depends on the charge density of the cationic polyelectrolyte. With lower charge density materials the binding to PPVS is weaker and binding of the dye to PPVS can occur before all of the polyelectrolyte charge has been neutralised. However, by carrying out titrations at several polyelectrolyte concentrations, good linear relationships were found, from which reliable charge density values could be derived. The streaming current method avoids the problem of competitive interaction of PPVS with o-toluidine blue and gives quite sharp transitions at the isoelectric point, although there was some dependence on polyelectrolyte charge density. This method gave good agreement with charge densities derived from the spectrophotometric technique. Effects of pH and ionic strength were also briefly investigated. For most of the cationic polyelectrolytes, there was some loss of charge at higher pH values, probably as a result of hydrolysis. Increasing ionic strength causes a less distinct colour change of o-toluidine blue, as a result of weaker electrostatic interactions.